Many particulate materials that are handled in bulk are stored in bins, silos, or similar vessels of various sizes and shapes. Examples of particulate materials that are stored in bulk in such vessels include coal; wood chips; sawdust; agricultural products such as grain, corn kernels, beans, flour, sugar, and peanuts; aggregate products such as sand and crushed stone; and industrial products such as plastic powders, coke, lime, silica gel, powdered acid resins, rare earth powders, and powdered alumina.
Storage vessels or containers for bulk particulate materials often include an unloading system that is associated with an outlet of the vessel. Such an unloading system may include a conveyor for transporting particulate material downstream for further processing. It is often necessary or desirable, when particulate material is unloaded from the storage vessel, to control the rate of discharge of particulate material from the storage vessel. Depending upon various factors, including the temperature, moisture content, permeability and compressibility of the particulate material, and the volume of particulate material stored in the vessel, the mass of particulate material in the vessel or container may compress that portion of the material at the bottom of the container proximate the discharge outlets. This compression can cause variations in the bulk density of the particulate material being unloaded, with the result that a discharge conveyor operating at a desired volumetric discharge rate may deliver a consistent volume of material but not a consistent mass of material, due to variations in bulk density of the particulate material. In addition, arching or bridging may occur in the vicinity of discharge outlets, when conditions are such that material in the vessel forms an arch, dome or bridge across or proximate to the outlet, especially when particulate material is stored to the capacity of the storage vessel. Arching or bridging may so restrict the flow of material through the outlet that it stops altogether. Under other circumstances, material may form a restricted open channel to the outlet, known as rat-holing, which limits the rate of discharge of material from the vessel in an uncontrolled manner.
Various assemblies and systems for bulk material storage and discharge are known in the art. In addition, various outlet designs are known for preventing arching or bridging at the outlet, or rat-holing. Nevertheless, conventional systems and assemblies often fail to provide a predictable and consistent volume and mass of unloading of particulate material from a storage vessel.
It would be desirable, therefore, if an apparatus and unloading system for a bulk material storage container assembly could be provided that would provide a predictable and consistent volume and mass of particulate material for downstream processing.